build: introduce declarative non-recursive build graph

1 files changed, 45 insertions, 0 deletions

diff --git a/scripts/build/run-if-changed.sh b/scripts/build/run-if-changed.sh
new file mode 100755
index 0000000..6cdc7c4
--- /dev/null
+++ b/scripts/build/run-if-changed.sh
@@ -0,0 +1,45 @@
+#!/bin/sh
+# SPDX-License-Identifier: GPL-2.0-or-later
+
+set -eu
+
+cmdfile=$1
+output=$2
+description=$3
+shift 3
+
+rebuild=false
+if [ ! -e "$output" ] || [ ! -e "$cmdfile" ]; then
+    rebuild=true
+fi
+
+while [ "$#" -gt 0 ] && [ "$1" != "--" ]; do
+    prerequisite=$1
+    shift
+    if [ "$prerequisite" != FORCE ] && [ -e "$prerequisite" ] && \
+       [ "$prerequisite" -nt "$output" ]; then
+        rebuild=true
+    fi
+done
+
+[ "$#" -gt 0 ] || { echo "run-if-changed: missing --" >&2; exit 2; }
+shift
+
+signature=$(printf '%s\0' "$@" | cksum)
+old_signature=
+if [ -e "$cmdfile" ]; then
+    old_signature=$(cat "$cmdfile")
+fi
+if [ "$signature" != "$old_signature" ]; then
+    rebuild=true
+fi
+
+if [ "$rebuild" = true ]; then
+    printf '  %s\n' "$description"
+    mkdir -p "$(dirname "$output")" "$(dirname "$cmdfile")"
+    "$@"
+    tmp="$cmdfile.tmp.$$"
+    printf '%s\n' "$signature" > "$tmp"
+    mv -f "$tmp" "$cmdfile"
+fi
+